1. Field of the Invention
The present invention relates to an information processing apparatus, a content providing system, an information processing method, and a computer program. In particular, the present invention relates to an information processing apparatus, a content providing system, an information processing method, and a computer program which perform data transmission via a network.
2. Description of the Related Art
DVDs are widely used as storage media with a large storage capacity. The DVDs are uses to store movie contents, for example. Blu-ray Discs (Registered Trademark of Sony Corporation), which use a blue laser, are an example of media with a greater storage capacity. The Blu-ray Disc (Registered Trademark of Sony Corporation) is capable of high-density recording, and of storing digital data of a large-size video content or the like with a high image quality.
A BD-ROM is a Blu-ray Disc (Registered Trademark of Sony Corporation) of the ROM type. BD-ROMs that store high-definition contents or the like have already been prevalent on the market. A user can mount such a medium storing a content on a playback apparatus, such as a personal computer (PC) or a disk player, to play the content. Rights to distribute music data, image data, and various other types of contents are generally owned by creators or distributors thereof. Accordingly, control, such as encryption, is placed on the contents when they are distributed, whereby some restrictions are placed on the use of the contents. Thus, the use of the contents is permitted for only authorized users, and unauthorized copying of the contents is prevented, for example.
Content using systems have been proposed that download, as subsequent data, additional data for a content recorded on a medium such as a DVD from a server, store the additional data in a storage unit such as a hard disk in a playback device such as the PC, and play the additional data in conjunction with the content recorded on the medium. Examples of such additional data include: subtitle data or dubbing data for a movie content; and service data or video or still image contents for other types of contents. Such content using systems are disclosed in Japanese Patent Laid-Open No. 2003-30157 and Japanese Patent Laid-Open No. 2001-126385, for example.
Features of a playback apparatus that plays the BD-ROM include a Java (registered trademark) execution environment called BD-J, a feature of connectivity to a server via a network using Java (registered trademark), and a feature of generating a single file system by integrating the subsequent data acquired from the server and stored in the hard disk, for example, with the content recorded on the disk for playback. The single file system generated by integrating the subsequent data with the content recorded on the disk is called a virtual file system (VFS). A playback process based on the VFS enables playback in a manner similar to that of a process of playing data on a single medium.
Use of the above features by executing a BD-J program supplied via a disk or a network achieves various processes, including the following processes:
(1) Acquiring a new AV content from a server and adding it;
(2) Changing an AV content on the disk by, for example, acquiring from a server a replacement content corresponding to the AV content on the disk; and
(3) Changing navigation corresponding to the content stored in the disk by acquiring, from a server, menu information, playback sequence information, or the like.
The Advanced Access Content System (AACS) is a standard for copyright protection of contents. The AACS defines a copyright protection technology based on a sophisticated common key cryptography (AES encryption). The AACS is described in AACS Common Book, Revision 0.91 AACS Recordable Video Book, Revision 0.91 (http://www.aacsla.com/specifications/specs091/AACS_Spec_Common—0.91.pdf) and AACS Blu-ray Disc prerecorded Book (http://www.aacsla.com/specifications/AACS_Spec_BD_Prerecorded—0.912.pdf), for example. The AACS provides specifications concerning encryption of the contents and use of cryptographic keys. In particular, the AACS specifies that different cryptographic keys should be used for different disk titles (e.g., movie titles), in order to improve security against leakage of the cryptographic keys, for example.
Examples of the subsequent data provided by the server include a movie advertising content called a trailer and service data. Some of such subsequent data are shared data to be provided for various titles of disk-stored contents to be provided to users. As described above, the AACS specifies that different cryptographic keys need be used for different disk titles, and accordingly the server that provides the subsequent data needs to encrypt the subsequent data with a cryptographic key corresponding to the disk title (e.g., movie title) owned by the user, and provide the encrypted subsequent data to the user. Therefore, when the number of titles for which the same subsequent data is to be provided is large, the server needs to generate or store a large number of different pieces of encrypted subsequent data for the same subsequent data, resulting in inefficient processing.